1. Technical Field
The present disclosure relates to lighting devices and luminaires, and in particular to a lighting device and a luminaire having a dimming function.
2. Description of the Related Art
A lighting device having a dimming function is known as a lighting device which supplies current to a solid-state light-emitting element such as a light emitting diode (LED). Such a lighting device includes a light dimmer, etc. for controlling a dimming ratio, and is capable of obtaining an arbitrary dimming ratio based on a user's operation performed on the light dimmer, etc.
In order to facilitate adjustment of brightness of light omitted from the lighting device having the dimming function, it is preferable that brightness perceived by a user linearly varies with respect to an amount of dimming operation performed by a user. However, human visibility characteristics are not proportional to a dimming ratio. For that reason, if the dimming ratio is made proportional to the amount of dimming operation performed by a user, it is not possible to linearly vary the brightness perceived by the user with respect to the amount of the user's operation.
In view of the above, a luminaire which receives a pulse width modulation (PWM) signal having a duty ratio proportional to the amount of a user's operation, and performs dimming of which a dimming ratio is proportional to approximately the 2.3th power of the duty ratio of the PWM signal is known (for example, Japanese Unexamined Patent Application Publication No. 2007-122944).